Official source code is out - https://groups.google.com/forum/#!topic/android-building/T4XZJCZnqF8
if I'm already on beta 1 and want to upgrade to beta 2, I just need to put the beta2 zipped rom into my internal sdcard and then use clockwordmod to flash it?
Correct; I just downloaded the Beta2 *update* ZIP (around 19MB), threw it ...
'Worked' as far as I can see, without having anyone to test it with. :-) I get the option to enable voice and video calls when changing my status, and 'voice call' appears as an option when talking to a contact.